Are piranha fish really as dangerous as the rumors say?

Featured in numerous horror films, the piranha is often depicted as a bloodthirsty and aggressive species with a terrifying killing speed.

Piranha is a freshwater fish primarily found in the southwestern region of Brazil, known for its moderate size. With its sharp jaws capable of tearing flesh in an instant, the piranha is also referred to as “saber-toothed fish.”

Close-up of the sharp jaws of a piranha.

This species has existed for a very long time on Earth, with fossils found in South America dating back around 25 million years. The modern piranha we see today, however, emerged approximately 1.8 million years ago.

Often depicted in Hollywood horror films, the saber-toothed fish is portrayed as a bloodthirsty and aggressive predator with a terrifying hunting speed. Therefore, when piranhas are mentioned, many people immediately associate them with fearful traits. But how much of this is actually true?

There are over 30 species of piranha living in the Amazon River basin. Most piranhas are considered the “devils” of the underwater world. Though they typically measure about 20 cm in length, they possess razor-sharp teeth like serrated blades, a powerful bite, and a tendency to live in schools. These characteristics make them one of the top predators in the Amazon River basin.

The lower jaw of a piranha with sharp teeth protruding.

Piranhas can easily bite through a five-layer aluminum can and can leave bite marks on extremely hard cow bones. Wherever there is a school of piranhas, there is an atmosphere of fear.

In the vicinity of the Amazon River basin, there are many fierce animals that instill fear in people, such as electric eels, crocodiles, giant otters, anacondas, and piranhas, with piranhas being the most feared of all.

The lower jaw of the piranha, with its knife-like teeth protruding, aligns perfectly with the upper jaw to form a guillotine-like shape. When biting, this jaw can quickly sever all the muscles of its prey.

Some species of piranha have two parallel rows of teeth on the upper jaw, with only six large teeth visible externally, while seven hidden fangs lurk inside.

Like most fish, piranhas do not chew and can sever a square piece of meat measuring three centimeters in a single bite. With their rapid swallowing ability, piranhas can easily consume prey much larger than themselves, sometimes dozens or hundreds of times their size. In just over 10 minutes, a school of piranhas can reduce their prey to a clean skeleton.

Like most fish, piranhas do not chew.

Piranhas have a thick back, and when viewed from the side, their head resembles an upright mountain with a tough layer of scales. This hard, keratinous scale layer serves as excellent protection against friction and external impacts and possesses strong regenerative capabilities.

On either side of the piranha’s body are lateral lines, which are important structures that allow them to sense water pressure and vibration frequencies. One end of the lateral line opens to the external environment through nerve conduits in the fish’s body, while the other end contains sensitive sensory cells. Therefore, this is also one of the most crucial hunting weapons of piranhas.

Piranhas are very sensitive to blood, odors, and decay, as the area above their mouths contains nostrils made of mucous membrane tissue. Thus, when blood or rotting carcasses are present in the water, piranhas are always the first to take notice.

Piranhas are very sensitive to blood.

During the breeding season, the coloration of piranhas changes. Some species of piranha that are initially red can transform their bodies into a rainbow-like color during breeding.

The female piranha will push aquatic plants aside to clear mud and then lay about 500 eggs in that spot. The male will swim above the eggs to fertilize them, and the fertilized eggs can hatch within two days. A few days later, the hatchlings will be ready to eat, measuring only about 1 cm, and at this stage, they will consume insects, crustaceans, small fish, and shrimp.

Some piranha species display cunning behavior and show little interest in their prey. When their prey becomes complacent, they will swiftly attack. Occasionally, piranhas also use aquatic plants for camouflage and ambush their prey.

A piranha caught in the Amazon River.

In reality, piranhas do not prefer to eat human flesh. They are not as dangerous to humans as depicted in films; they are merely “killers” to smaller prey.

In real life, piranhas are relatively calm. They are not overly aggressive species. Most of them eat insects, worms, small plants, or small fish found in their river habitats. Only a few species of saber-toothed fish are attracted to the smell of blood and will seek out prey of comparable size.

Watch a hungry school of piranhas “devour” meat in an instant.

Previously, in a video recorded by BBC filmmakers, a test was conducted by dropping a piece of meat into the water to observe the reaction of the school of fish. The footage shows that, thanks to their exceptionally quick sense of smell, the piranhas rapidly detected the “prey” and began to tear at it with astonishing speed.

A hypothetical scene if one were to fall into a pool full of piranhas.

Returning to the initial hypothetical question: What would happen if we accidentally fell into a pool filled with piranhas? The reality is, you might actually scare them. Piranhas are not truly “interested” in humans unless they are very hungry and the person is already dead.

Today, many people still keep piranhas as aquarium pets, but for safety reasons, keeping piranhas in tanks is considered extremely dangerous and should not be attempted. Piranhas are an invasive species that can easily harm humans and disrupt local ecosystems.

Despite their fearsome name, piranhas also have positive roles; they help clean dead animals from rivers and purify the water. Some piranhas eat only fruit, which can carry seeds to other areas where they can take root and sprout, promoting species diversity.

Additionally, the flesh of piranhas is quite delicious, often considered tastier than most fish, making them a favorite catch for locals. Indigenous people even use piranha teeth to make bows, knives, and even hair cutting tools.